The effect of endotoxin shock on the distribution of gastric blood flow was measured with radioactive microspheres in a swine stress ulcer model. Ten piglets were shocked with intravenously administered Escherichia coli endotoxin and compared with six controls. Blood flow was calculated before and after shock by assaying 2-cm square sections of stomach. Distribution of gastric blood flow was analyzed graphically and ischemic regions were compared to ulcerated areas. Endotoxin caused a redistribution of gastric blood flow which did not parallel cardiac output change. Ischemia was maximum in the corpus where flow per gram decreased 62.2%, and stress ulcers developed only in this region in all shocked animals. There were no ulcers in controls where gastric blood flow paralleled cardiac output. Endotoxin caused a selective regional gastric ischemia unlike the diffuse, patchy flow seen following hemorrhage.